Abstract: In this paper, with assumption that the stratified ocean consists of two layer fluidswith different densities, the problem of the second order wave diffraction by threedimensional bodies in the stratifed ocean is investigated With the use of the regularperturbation method. the boundary value problem of the second order multi-chromaticwave scattering potential is firstly formulated, and is based on a weakly radiationcondition, a formal solution Of this boundary value problem is then found. By usingGreen theorem and introducing an assisting potential, the integral expressions, whichdo not explicitly connect with the second order scattering potential, of the second orderwave loads are also derived. Our analysis indicates that the effects of the stratificationupon the second order difference frequency wave loads on the structures may besignificant.

Key words: wave diffraction and scattering, shipbuilding and offshoreengineering, wave loads, nonlinear water waves, internal waves